Silver lithium alloy



Patented Apr. 9, 194i) UNITED STATES PATENT; OFFICE. I sILvEn LrrnnJMALLOY I Fran! R; Hensel, Kenneth L. Emmett, andlllnel P. B. Mallory -82.

a corporation of It is an object of the present invention to provide analloy which has improved electrical properties such as electricalconductivity.

It is a further object or the present invention to provide an alloywhich shows great fluidity in the molten state and lends itself tocasting ofvery intricate shapes. I

It is a still further object of the present in-' vention to produce analloy which has improved wetting characteristics whenused as a silversolder. g

Another object of the present invention is to produce a new alloy whichhassuperior electrical characteristics when used as an electricalmakeand-break contact such as low material transfer,

low contact resistance and freedomfrom welding or sticking.

Other objects of the invention willbe apparent i'rcm the followingdescription taken in connection with the appended claims. The presentinvention comprises the combination of elements,.

methods of manufacture and-the product thereof brought out andexemplified in the disclosure "hereinafter set forth, the scope of theinvention being indicated in the appended claims. 4 While I a preferredembodiment of the invention is described herein, it is contemplated thatconsiderable variation may be made in the method of procedure and thecombination of elements with- 40 out departing from the spirit of theinvention.

The present invention contemplates the addition to silver of lithium andmetal from the group consisting of cadmium and zinc. .It is contemplatedthat alloys may be produced according to the invention ha'vlngthe-ingredients combined in the following range of proportions:

1 Percent Lithium .002to 8 Metal selected from the group consisting ofcadmium and zinc 1 mill) Balance, substantially all silver.

Wehave also mind that the addition of-the following elements-may improvethe V gether in the correct proportions.

W. Wiggs, Indianapolis, Ind., assignorl to 00., Inc., Indianapolis,1116.,

Application December 18, '1 939.

Serial No. 303,996 I K tics of the present alloyscovered by the presentinvention: I

. Per cent Tll'l Up to 11 Manganese Up to 20 3 Nickel Up to 10 Phosphorv p v Up to 8 Silicon Up to 2 It is also possible to substitute copperfor a substantial part of the silver. I t

A A number of preferred compositions are given below: v a

Per'cent l. Cadmium 20 u Lithium .01 Silver Balance 3 Silver- 50 Cadmium18 Zine Ooppe'r 15.2 ldthinm I v I 3 26' s. Silver .53. I

Zine 16 Copper 30.75

' Lithium .25

5. Silver 60 7.1 l5 Copper 20 Nickel 4.75 Lithium .25

- In addition to the baser elements, materials 35- from the palladium,platinum or gold group may also be present up to 10% each. The alloys ofthe present invention are preferably prepared by melting the ingredientsto- The lithium 40 is preferably added in the form of a silverlithiummaster alloy, containing approximately 15% of lithium. This master alloyhas a very low melting point which is in the neighborhood of 410 to 450C. and therefore will so readily 4.5 into solution when added to thesilver-copper melt.

The effect of lithium is to completely deoxidize the silver melt and tofree same from other impurities which are harmful. Part of the lithiumso will be eliminated together with these impurities and the remainingmelt will be free from inclusions and oxides. The presence of lithiumalso prevents the further oxidization of the melt during the heatingperiods to which the melt may be u I it.

I subjected and the material retains a very high fluidity duringpouring, resulting in extremely clean castings.

We have found that cadmium-silver alloys orv f silver-zinc alloys e. g.containing a small percentage of lithium such as, for instance, .01%or'less will lend themselves much more readily to rolling and wiredrawing operations, resulting in a material which is entirely free fromsurfaceblemishes and oxide stringers. Furthermore if such silver wire isbeing spun or ii silver wire produced in that manner is being headed, asurface finish can be obtained with alloys of the new in-' vention thatexcels anything obtainable so far with alloys of the prior art. Veryoften in heading of silver alloys containing elements of the secondgroup of the periodic system,' the formation of edge cracks or splits isencountered, causing a great number of rejects. By the addition oflithium to these alloys in the proportions specified these difilcultiescan be eliminated or materially reduced.

If lithium is used inhigher proportions such as .05 to 1% it was foundthat alloys of silver with elements of the cadmium-zinc group will showgreatly improved-electrical characteristics. Contact alloys of this typehave very improved characteristics as far as material transfer andcontact resistance are concerned. It was also of great interest to findthat the material transfer for this composition was from the cathode tothe anode. In most silver base alloys the material transfer is in theopposite direction, therefore it seems desirable to use the material ofthe present invention in combination with another silver alloy havingopposite transfer characteristics.

We have carried out ments with compositions containing zinc and cadmium,to which was added 25% lithium. After the material-was rolled into sheetor drawn a large number of experiinto wire, tests were made using thesealloys for silver soldering purposes. It was found that most excellentresults were produced by these new combinations. In order to cheapen thesilver solders or to lower the melting point by the formation of ternaryor quaternary eutectics, it was found that the addition of copper couldbe made to replace a substantial portion of the silver. It was alsofound that the addition of such elements, as particularly manganese,tin, phosphorus and silver would further improve the performance of thealloys containing 25% of lithium when used for silver solderingpurposes. The alloys will flow very readily and will wet the metals tobe joined readily and produce a joint of very high physical strength.

Since lithium decreases the melting point of silver very materially andsince an eutectic is formed at 2.7% lithium, having a melting point of610 C. care must be exercised when these materials are processed atelevated temperatures and if they contain higher percentages of lithium.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof,-it isnot desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy containing .002 to 3% lithium, 1 to 30% of an elementselected from the group consisting of cadmium and zinc and the balancesubstantially all silver. 7

2. An alloy composed of .05 to 1% lithium, 1 to 30% of an elementselected from the group consisting of cadmium and zinc and the balancesilver.

FRANZ R. HENSEL. KENNETH L. EMMERT. JAMES W. WIGGS.

